Various antitumor substances have been developed for use in the treatment of malignant tumors which are now the most highest cause of death. Among these substances, an antitumor platinum compound, cisplatin, has a broad range of antitumor spectrum and takes an important role in the chemotherapy of various tumors. However, cisplatin has a problem of causing side effects such as renal toxicity, blood toxicity, digestive organ toxicity, nervous toxicity and the like. In consequence, attempts have been made to develop antitumor agents which have low toxicity and high antitumor effects.
For example, it has been reported that a compound in which platinum is coordinated to 1,2-diaminocyclohexane has excellent antitumor effect and relatively high safety (JP-A-2-212497, JP-B-3-66318 and JP-B-4-79353; the terms "JP-A" and "JP-B" as used herein respectively means an "unexamined published Japanese patent application" and an "examined Japanese patent publication").
These antitumor substances, however, have disadvantages in that their pharmacological effects and safety are not always satisfactory and their administration by injection are limited because of their low solubility in water.